The AN-32 transport aircraft of the Indian Air Force that went missing with 29 passengers on board on July 22 did not have an underwater locator beacon on it. It has therefore become even more difficult for search teams to look for the aircraft, reported The Indian Express.

The underwater beacon, which is usually integrated with a Flight Data Recorder in the cockpit, would have helped locate it in the event of a crash in the Bay of Bengal. The search team is now left with only one option: to use sonar signals that reflect off a metallic surface under water. However, such an operation is both time-consuming and has a very low success rate.

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The underwater beacon emits ultra-low level frequencies that can travel through water. These frequencies can be tracked by submarines and other underwater vessels. Most importantly, the battery of a ULB lasts for a month. Almost all modern aircraft are equipped with this device.

The missing AN-32 had two Emergency Locator Transmitters, but their battery life was estimated at around 72 hours, and they do not function under water. Besides, Defence Minister Manohar Parrikar said that the ELT would get activated only if the aircraft hit water with a force of 20 G, reported IANS. The aircraft also had four life rafts fitted with a Personal Locator Beacon that transmits signals on coming in contact with water. However, these also operate only on the surface of the sea and have a very short battery life.

India has sought the help of the United States to locate the missing plane. The IAF has decided to immediately install this device on all AN-32s that operate over water, reported NDTV.